By: Christie Potter

Probabilities

Bailey Weaver “88 Kings and Queens” Oct 25, 2009 via Flickr, Creative Commons Attribution

What is a probability?Three major points

1.An experiment (Situation)

2.An outcome (Result)

3.An event (Single Result)

Probability=

measurement of a single event occurring

• 0=NO chance of the probability occurring

• In Between = represented with fractions, decimals, &

percent

• 1=the probability WILL occur

0-1 Probability

• Percent: 0-100% probability• Decimal: 0.0-1.0 probability• Fraction: 0/1 - 1/1 probability• Each can be interchangeable

Using Fractions, Decimals, &

Percent

Example: 20%

• Fraction 20/100 can be SIMPLIFIED to 1/5

• Decimal 20% DIVDED by 100% = .2

Starting At A Percent

Example: ¾

• Percent ¾ is EQUAL to 75/100 or 75%

• Decimal 3 DIVIDED by 4 equals .75

Starting At A Fraction

Example: .5

• Percent .5 MULTIPLIED by 100 = 50%

• Fraction 50/100 can be SIMPLIFIED to ½

Starting At A Decimal

# of ways event can occur

P (A) = total # of possible outcomes

Where A = The Event

Probability of an Event

• IF P (A) > P (B)

• THEN A is more likely to occur

• IF P(A) = P(B)

• THEN P (AB) are equally likely to occur

Probability A vs. B

Dice Example

• Probability (1/6)

- for each number 1-6

• 1 = each number on a die

(1,2,3,4,5,6)

• 6 = total number of sides

Continued…

We Can Also Say…

•Probability of EVEN numbers:•P (3/6) OR (1/3)

•Probability of ODD numbers:•P (3/6) OR (1/3)

Leah Love “Dice Isn’t Just A Game; It’s a Way of Life” Aug 18, 2005 via Flickr, Creative Commons

Attribution

•P (Yellow) = ¼

•P (Blue) = ¼

•P (Green) = ¼

•P (Red) = ¼

A Spinner Example

•Used when drawing from a bag

•Take object out without putting back

•Carton has 12 eggs

• I take one

• 11 are left

Probability Without Replacement

• I have 30 pieces

•7 are Red

•23 are Blue

•I’m going to pass them out

Jar of Candy

Ella Novak “Jar of Candy” Jan 5, 2003 via Flickr, Creative Commons Attribution

Creating A Probability Tree

Candy

P (Red) 7/30

P (Blue) 23/30

P (Red) 6/29

P (Blue)23/29

P (Red)7/29

P (Blue

)22/29

•P (Red, Red) : 7/30 MULTIPLY by 6/29

= 42/870

•P (Red, Blue) : 7/30 MULTIPLY by 23/29

= 161/870

•P (Blue, Blue) : 23/30 MULTIPLY by 22/29

= 506/870

•P (Blue, Red) : 23/30 MULTIPLY by 7/29

= 161/870

The Math

•Q: Which is MOST likely to occur?

•A: P (Blue, Blue)

•Q: Which is LEAST likely to occur?

•A: P (Red, Red)

•Which are EQUALLY likely to occur?

•A: P (Red, Blue) & P (Blue, Red)

Q & A